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For a week, Sanford has been talking up Shealy in TV ads paid for by Carolinians for Change, one of the groups promoting Sanford's agenda. He came out early against incumbent Sen. Jake Knotts, a frequent critic, calling him a “Republican in name only.”

Knotts' campaign manager Rod Shealy says it's an extremely close race. Two weeks ago one of his clients, state Sen. Catherine Ceips, fell to Sanford-backed Tom Davis – a Sanford buddy for years who served as chief of staff and on state boards for the governor.

Shealy said Knotts' race is different. “A lot of people Jake Knotts has helped over the years are now coming forward to help Jake get re-elected,” Shealy said, including U.S. Rep. Joe Wilson, one of the county's most beloved Republicans, who held the seat before Knotts.

In the Upstate, big money and immigration are playing out in a couple of Senate races centered in Spartanburg County.

State Rep. Scott Talley has the backing of U.S. Sen. Jim DeMint and some of the state's wealthiest Republicans, while opponent Lee Bright has Sanford and interests with plenty of money on his side, including those third-party groups pushing Sanford's agenda.

State Sen. Jim Ritchie is also in a runoff against Shane Martin.

If history predicts outcomes, Sanford's favorites have the odds in their favor. Five Statehouse Republicans have lost in runoffs since 2002.

Those losses seem to run against common wisdom that money and visibility give incumbents an advantage.

Ritchie sees things other than money at play, saying an anti-incumbent sentiment may come from “the combination of frustration among folks with gas prices and immigration and people expressing their frustration at the ballot box.”

Voters who cast ballots in the June 10 primary can vote only in the same party's runoff — people who voted in the Democratic primary can't cast Republican runoff ballots.

On the other hand, people who did not vote June 10 can vote in either party's runoff. That makes them a key target for candidates.

That strategy seems to work. In 18 primary runoffs for Statehouse seats since 2002, turnout increased an average of 12 percent with more ballots cast in all but two contests.

South Carolina is one of fewer than a dozen states that require a runoff in party primaries if no candidate gets a majority of votes, according to FairVote, a Maryland group advocating for primary election law changes. Most states simply advance the top vote getter to the general election.